Geographically linked images provided as a database are useful in, for example, real estate marketing, municipal property tax assessment, utility company asset inventory collection, map-related visual cues for use in navigation or advertising, virtual tours of a neighborhood, etc. These images are desirably taken from a surface level perspective using a high resolution digital camera in order to create a digitally appealing result that can be displayed in a wide range of sizes and levels of image compression. Due to the large number of images being acquired in order to build a useful database, it is desirable to collect the images quickly using a moving vehicle, for example an automobile, boat, motorcycle, etc. To minimize the cost and time associated in building and updating the image database, it is desirable to employ teams of relatively unskilled workers using vehicles that are rented or leased for a short period of time in a particular location (e.g.: a particular city). Training time and vehicle modification are therefore to be avoided. The system should use commercially available components wherever possible, be portable, easy to repair and easy operate.
Previous attempts to automate image collection have employed video cameras. The audio track in the video recording is normally used to store position or time information in association with the images. The low quality image resolution provided by inexpensive video cameras limits the usefulness of the acquired images and it is desirable to avoid the cost and complexity of more expensive video cameras. Furthermore, it is difficult in practice to relate the location of a particular frame or series of frames in a video to an accurate geographic location, further limiting the usefulness of such a system. Examples of video based mobile image acquisition systems are disclosed in the following U.S. Pat. Nos. 5,633,946; 6,335,754; 6,363,161; 6,571,052, 6,741,790; and, 6,950,120. Video cameras acquire images continuously while in operation and no discrete photo request is needed to instruct the camera to acquire an image at a particular location.
In acquiring a large number of surface level digital images, it is desirable to use a moving vehicle equipped with a computer system including automated image collection software that relates the images to geographic position data; however, there are a number of difficulties encountered in creating and implementing such a system. Although the global positioning satellite (GPS) system offers geographic position data, the accuracy of the system is limited; this accuracy is reduced in a moving vehicle, since commercial GPS equipment reports position on an averaged basis and samples too infrequently to provide accurate position data while in motion. The low sampling rate also makes it difficult to predict the spacing (distance) between images as a function of time only, which introduces problems during post-processing. It is therefore desirable to enhance the GPS position data in order to obtain an accurate image location and spacing. Examples of systems for enhancing GPS location of moving vehicles, albeit not in connection with image acquisition, are provided in the following U.S. Pat. Nos. 6,061,627; and, 5,796,613.
In addition, it is desirable in such a system to use a commonly available digital camera to reduce system cost and to provide easy replacement in the event of camera malfunction. These cameras typically store the images within localized digital memory and do not commonly transmit the images to a computer in real-time; the transmission of images is made even more difficult when high resolution images are acquired, since the size of these images creates additional delay during transfer. The images stored locally on the camera cannot presently be tagged with the position data stored on the computer. A method of relating the separately stored image and position data is therefore needed. Examples of systems using still cameras are provided in the following U.S. Pat. Nos. 7,155,336; and, 6,233,523.
U.S. Pat. No. 7,155,336 discloses a system using synchronized time clocks on the camera and computer in order to later correlate the time-indexed images with time-indexed position information; however, synchronization between devices adds complexity to the system and can introduce image position errors if not maintained continuously. It is worthwhile noting that the use of synchronized clocks obviates the need for storing photo requests or responses on the computer for later use in correlating time values between the camera and computer.
U.S. Pat. No. 6,233,523 relies on manual entry of house number information by an observer, either verbally or using a keyboard, to correlate images and position information; therefore, it is not necessary to store photo requests or responses for later linking of this information. When still image cameras are employed, it is described that the vehicle is stopped in front of each location where it is desired to acquire an image; images are therefore not acquired from a moving vehicle, which limits overall throughput.
Since a moving vehicle may not always travel in a straight path, the orientation of the camera can change, making it difficult to correct the image to a consistent perspective. It is therefore desirable to collect information on camera orientation and relate that information to the image being collected in order to simplify image perspective correction.
In order to overcome some or all of the above problems in the art, an improved method of acquiring geographically related digital images is needed.